Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 35-07: Amebiasis + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Fever, abdominal pain Amoebae or antigen in stool or abscess aspirate Positive serologic tests but may represent prior infections Hepatomegaly, hepatic abscess on imaging studies +++ General Considerations ++ The Entamoeba complex contains three morphologically identical species E dispar, which is avirulent E moshkovskii, which is also avirulent E histolytica, which may be an avirulent intestinal commensal or lead to serious disease Humans are the only established host for E histolytica Transmission occurs through ingestion of cysts from fecally contaminated food or water Infection can be transmitted person-to-person Flies and other arthropods also serve as mechanical vectors Disease follows penetration of the intestinal wall, resulting in Diarrhea Dysentery Extraintestinal disease, most commonly liver abscess +++ Demographics ++ E histolytica infections are present worldwide but are most prevalent in subtropical and tropical areas under conditions of crowding, poor sanitation, and poor nutrition Of 500 million persons worldwide infected with Entamoeba, most are infected with E dispar and an estimated 10% (50 million) are infected with E histolytica Mortality from invasive E histolytica is about 100,000 per year Severe disease is more common in Young children Pregnant women Persons who are malnourished Persons receiving corticosteroids Hepatic abscesses more common in men + Clinical Findings Download Section PDF Listen +++ +++ Symptoms and Signs ++ Many patients do not have current or a past history of intestinal symptoms Acute or gradual onset of abdominal pain Fever Enlarged and tender liver Anorexia Weight loss Intercostal tenderness Diarrhea is present in a small number of patients Abscesses are most commonly single and in the right lobe of the liver Amebic infections may rarely occur throughout the body, including the lungs, brain, and genitourinary system +++ Differential Diagnosis ++ Pyogenic liver abscess Echinococcosis (hydatid disease) Cholecystitis or cholangitis Right lower lobe pneumonia Pancreatitis Hepatocellular carcinoma + Diagnosis Download Section PDF Listen +++ +++ Laboratory Tests ++ Leukocytosis and elevated liver biochemical tests Serologic tests for anti-amebic antibodies are almost always positive, except very early in the infection Thus, a negative test in a suspicious case should be repeated in about a week The stool E histolytica antigen test is positive in ~40% of cases; the TechLab II test can also be used to test serum, with good sensitivity if used before the initiation of therapy Examination of stools for the organisms or antigen is frequently negative +++ Imaging Studies ++ Ultrasonography, CT, or MRI show abscesses as round or oval low-density nonhomogeneous lesions with abrupt transition from normal liver to the lesion and hypoechoic centers +++ Diagnostic Procedures ++ Percutaneous aspiration May be needed to distinguish between amebic and pyogenic abscesses Best done by an image-guided needle Typically yields brown or yellow fluid Detection of organisms in the aspirate is uncommon, but detection of E histolytica antigen is very sensitive and diagnostic The key risk is peritoneal spillage leading to peritonitis from amoebae or other (pyogenic or echinococcal) organisms + Treatment Download Section PDF Listen +++ +++ Medications ++ See Table 35–6 Treatment is tinidazole or metronidazole plus a luminal agent Intravenous metronidazole can be used when necessary If initial treatment with metronidazole or tinidazole fails, add chloroquine, emetine, or dehydroemetine Neither emetine nor dehydroemetine are available in the United States +++ Therapeutic Procedures ++ Needle aspiration may be helpful for large abscesses (over 5–10 cm), in particular if The diagnosis remains uncertain There is an initial lack of response Patient is very ill, suggesting imminent abscess rupture + Outcome Download Section PDF Listen +++ +++ Complications ++ Without prompt treatment, amebic abscesses may rupture into the pleural, peritoneal, or pericardial space, which is often fatal +++ Prognosis ++ With successful therapy, abscesses disappear slowly (over months) +++ Prevention ++ Safe water supplies; water can be Boiled Treated with iodine (0.5 mL tincture of iodine per liter for 20 min; cysts are resistant to standard concentration of chlorine) Filtered Sanitary disposal of human feces Adequate cooking of foods Protection of foods from fly contamination Handwashing In endemic areas, avoidance of foods that cannot be cooked or peeled +++ When to Admit ++ All patients should be admitted + References Download Section PDF Listen +++ + +Pandey S et al. Comparative study of tinidazole versus metronidazole in treatment of amebic liver abscess: a randomized control trial. Indian J Gastroenterol. 2018 May;37(3):196–201. [PubMed: 29948994] + +Saidin S et al. Update on laboratory diagnosis of amoebiasis. Eur J Clin Microbiol Infect Dis. 2019 Jan;38(1):15–38. [PubMed: 30255429] + +Shirley DT et al. A review of the global burden, new diagnostics, and current therapeutics for amebiasis. Open Forum Infect Dis. 2018 Jul 5;5(7):ofy161. [PubMed: 30046644]